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Mixing Voltages

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Xenobius

New Member
Hello all, This is my first post here :)

I have a project at the moment and everything is to work from a single 12V battery. Now I am using an Arduino which has its own 5V regulator. Since I intend to switch some ICs and a relay, I can't just power everything from this poor 5v regulator.

1. Can I for example have a transistor's base switch on using the output from the uC (Arduino), have the emitter connected to GND, and the collector-relay-coil take voltage directly from the battery?

2. Another similar scenario is to have two 5V regulators (1 on Arduino and 1 for some ICs) both of which taking power from 12V battery and have the Arduino "mix" its 5V with that of the ICs ?? For example the ICS are powered from a 2nd V regulator while they receive input pulses from the uC using the 1st V regulator...

Sorry if this is silly but I know that this might be fatal to some components in certain circumstances.

Thanks
X
 

Brevor

Member
1. Can I for example have a transistor's base switch on using the output from the uC (Arduino), have the emitter connected to GND, and the collector-relay-coil take voltage directly from the battery?

2. Another similar scenario is to have two 5V regulators (1 on Arduino and 1 for some ICs) both of which taking power from 12V battery and have the Arduino "mix" its 5V with that of the ICs ?? For example the ICS are powered from a 2nd V regulator while they receive input pulses from the uC using the 1st V regulator...

Yes you can do both.
 
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Xenobius

New Member
Wow thanks for your super fast reply. So can you specify any other scenario where connecting separate voltages can actually destroy a device? Because this is haunting me constantly.

Thanks once again
 

Diver300

Well-Known Member
Most Helpful Member
If the supplies are not connected at all, then you can't mix the voltages. For instance, you can't have an Arduino measure mains voltage (even via a suitable voltage divider) and have the Arduino connected to ground.

In your case, the grounds of the two 5 V supplies and the 12 V supply are already the same point, so that is fine.

It is more difficult if you want to switch the positive, rather the negative that you are switching.

You can get a problem if one 5 V supply is there and the other isn't. That could lead to an input on the Arduino being at a higher voltage that its supply, or a high output on the Arduino trying to power what is effectively a short circuit.

A fault on one 5 V supply, or even different turn-on and turn-off rates can lead to problems.
 

Xenobius

New Member
Oh ic, this is now much clearer thanks a lot for your replies guys :) I like this forum mhux better. I think I'll actually stick to it and become a contributor!!

Thanks
 
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